Why do we need plinth beams

Basic thresholds in half-timbered houses

The basic sleepers of half-timbered houses are usually made of English oak or sessile oak, a wood that is durable against fungus and insects - if there is no waterlogging.

Often the threshold in the splash zone is installed too close to the ground. In this zone, 30 to 40 cm above the ground level, waterlogged water and dirt deposits form persistent waterlogging on the surface. The water that is drawn into the soiled uprising joint creates an additional load.

In order to reduce these harmful conditions, constructive protective measures are necessary.

The foundation level should stand back under the threshold. The threshold can protrude 2 to 3 cm. A sharp edge cut forms the drip edge (a groove weakens the edge and hardly survives the construction phase without damage).

The underlying foundation allows a threshold overhang of 2 to 3 cm. Even a sharp cut edge creates a drip nose.
Photo: Rüpke

Cardboard as a barrier on the sleeper substructure is not necessary, even if the foundation material has a capillary effect. A deliberate air gap under the threshold makes more sense and is sufficiently safe.

If cardboard is built in, it must be undercut, otherwise water drawn into the narrow uprising joint (shooting joint) will form permanent waterlogging under the threshold, which also dries out poorly due to the location (vegetation).

Due to their location, mostly in the area of ​​the splash zone, ground sleepers are therefore a "wear and tear" not only of historic half-timbered houses. They are exposed to a particularly high degree of "double exposure" from splash water, moisture from the base and sometimes from moisture from the inside that becomes effective due to usage. They therefore usually have a "shorter" lifespan of approx. 80 to 120 years and therefore have to be replaced more often.

However, the moisture load could be carefully minimized through structural measures, if not even prevented entirely, e.g. through well-considered planning. This increased the lifespan of the sleepers. In fact, it is essential if you consider various aspects, which we want to illustrate in more detail below with the help of photos.

The roofing felt under the threshold should act as a moisture barrier between the "damp" sandstone base and the threshold. But because the cardboard protrudes, it inevitably leads water under the threshold! The sandstone itself hardly carries any water. The ivy growth prevents drying. No cardboard is better!
Photo: Dr. Kürsten
Here "damaging" a cardboard on the molded brick roll layer. A few millimeters of the cardboard is enough for water to run into it. Just 4 years old, and due to the sapwood on the leading edge, there was already fungal damage (white rot, Donkioporia expansa).
Photo: Rüpke

On both images above, a roofing felt can be seen, which acts as a moisture barrier between the damp base and the threshold. However, this roofing felt protrudes so far that water can run under the threshold on it. In this respect, the cardboard is damaging. An open air joint is structurally correct and reduces the moisture load due to rapid drying out.

Not only half-timbering is polluted in the splash water area and exposed to the weather. Many unsuccessful measures on this house wall testify to the lack of understanding of it. Locking means were the builder's answer. He wanted splash protection, he built up the water vapor pressure and thus created new damage inside.
Photo: Rüpke
Here the basic inner threshold is only present as dust. Installed behind an installation base made of screed concrete, the fungal attack is now over with the total collapse of the oak threshold. The cause was the accumulation of condensation in the cold area close to the ground, which could not ventilate and thus dry because of the non-capillary action of the concrete.
Photo: Rüpke
The soil reaching to the threshold led to waterlogging here. Eichenporling, and allied with it the colorful rodent beetle, takes advantage of the good conditions on offer and nibbles on the oak beams. Located only 30 cm higher, away from splashing water and dirt, the oak would have offered sufficient resistance. Photo: Rüpke

The "blocking" of sleepers by raising the levels externally or internally rarely happens in Intention. Rather, it is thoughtless later construction measures that create such conditions and always end with a total loss of the built-up threshold. For the actual hazard (hazard class 4, wood freely weathered with contact with the ground), the durability of the wood type oak (resistance or durability class 2 = permanent) is no longer sufficient here. Only very durable wood would have a relative chance of survival here. Unfortunately there is no such wood in Europe ... Due to the nature of things, there is no such thing as durable wood anyway. It is only our art of building that can make wood a long-lasting building material. Until not so long ago, our architecture had proven itself well, as we can prove with the preserved medieval inventory. Why not keep it up?

A ground-level terrace and the required freedom from splashing water for the oak ground sill - they never go together. It requires stopgap solutions. Here the pollution is reduced by a lowering with coarse gravel bed and a water flow (recognizable the important flush pipe!) Photo: Rüpke

Actually reducing the weather exposure through constructive measures is a worthwhile way. The design of the construction is adapted to the given durability of the wood. This is done here by lowering the spray water load and the evaporation horizon of the foundation wall environment. As I said, there is one way ... the "ways to Rome" are known to be many.

Often it is the client's ideas that the design of the dream house has to follow. It is precisely here that the planner makes wrong compromises. At least one explanation of the building owner about the effects of ground level access would have been necessary in the example.

If the oak threshold in the splash water area is 30-40 cm above the ground, every emergency measure that helps to reduce the burden helps. Here it is a drainage channel ...
Photo: Rüpke
An oak sleeper with cardboard at floor level. The channel in front of it is supposed to lessen the weather exposure a little. The water ingress into the mortises was drained away.
Photo: Rüpke
The podium in front of the house? There is pollution from splash water and waterlogging. A constructive solution here is limited to the separation of brick and wood. The client's will is always decisive. Photo: Rüpke

The pictures above are intended to show that the measures that would be necessary as examples are not always possible. Then it is time to use all of the possibilities in order to get closer to the goal of reducing the weather stress little by little. One must also see the given circumstances, which are determined by the will of the builder. But an explanation is the best way to a "later" insight.

A wall structure above the threshold: brickwork, clay-bonded core insulation, inside an aerated concrete shell with a dense tile covering. Behind the kitchen. The structure blocked the path of condensation in the aerated concrete. The interior insulation "drowned" afterwards. New oak sleepers and handles then fell victim to the oak spear. Photo: RüpkeAlso endangered basic thresholds. Here on both sides under the central bulkheads in the hallway. The dense stone covering is both a condensation level and a seal. Condensation in the ground and on the threshold can no longer come out. Base tiles secure this. Once there was a rammed earth floor that was very effective with capillary action ... Photo: Rüpke

The threshold can also be endangered from above if, as in the picture above left, a large amount of condensation occurs in the compartment due to the construction and use. Above right picture: The basic thresholds in the building, which are not visible to the layperson, have been lost, and have disappeared over the years due to increasingly higher floor structures. In fact, they are already here all over the place Length all rotten.

After an infestation by the real dry rot, constructive weaknesses were revealed in the swelling area. Dense tile cladding (in front of the area exposed to moisture) made it difficult for moisture to penetrate into the interior. The expanded clay fill was completely covered with sponge. Photo: Rüpke Here is the same area after the sponge renovation. In an air shaft in front of the threshold, a heater with convection is built in. The inner installation cladding is now made of clay masonry with a capillary effect. On top of the vault, the floorboards follow the sand pouring.
Photo: Rüpke

A load on the outer basic threshold is also increased so much by an internal construction (in the pictures above in a bathroom area) that the natural durability of the oak is no longer sufficient to withstand the attack of wood-destroying fungi. The cladding visible in the picture on the left had a particularly damaging effect; it was like a stagnant layer of air and precluded any transport of water from the surrounding area of ​​the threshold to the inside (the last possible way out). There was considerable damage here.

It looks romantic, this watering hole - but it is the death of the oak threshold behind it. The splash water already strains the plastered areas, the vegetation prevents wind and sun from entering. It has already been heavily repaired here - but without any effect.
Photo: Rüpke
The threshold is defenseless against waterlogging caused by splash water and dirt and is shaded by vegetation. The oak sill is increasingly prevented from drying off, in the end it becomes impossible. Total loss is preprogrammed. Photo: Rüpke

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